cgroup: reorder the operations in cgroup_destroy_locked()
This patch reorders the operations in cgroup_destroy_locked() such
that the userland visible parts happen before css offlining and
removal from the ->sibling list. This will be used to make css use
percpu refcnt.
While at it, split out CGRP_DEAD related comment from the refcnt
deactivation one and correct / clarify how different guarantees are
met.
While this patch changes the specific order of operations, it
shouldn't cause any noticeable behavior difference.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 49bfd7b..5a1ddec 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4379,13 +4379,8 @@
/*
* Block new css_tryget() by deactivating refcnt and mark @cgrp
- * removed. This makes future css_tryget() and child creation
- * attempts fail thus maintaining the removal conditions verified
- * above.
- *
- * Note that CGRP_DEAD assertion is depended upon by
- * cgroup_next_sibling() to resume iteration after dropping RCU
- * read lock. See cgroup_next_sibling() for details.
+ * removed. This makes future css_tryget() attempts fail which we
+ * guarantee to ->css_offline() callbacks.
*/
for_each_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
@@ -4393,8 +4388,41 @@
WARN_ON(atomic_read(&css->refcnt) < 0);
atomic_add(CSS_DEACT_BIAS, &css->refcnt);
}
+
+ /*
+ * Mark @cgrp dead. This prevents further task migration and child
+ * creation by disabling cgroup_lock_live_group(). Note that
+ * CGRP_DEAD assertion is depended upon by cgroup_next_sibling() to
+ * resume iteration after dropping RCU read lock. See
+ * cgroup_next_sibling() for details.
+ */
set_bit(CGRP_DEAD, &cgrp->flags);
+ /* CGRP_DEAD is set, remove from ->release_list for the last time */
+ raw_spin_lock(&release_list_lock);
+ if (!list_empty(&cgrp->release_list))
+ list_del_init(&cgrp->release_list);
+ raw_spin_unlock(&release_list_lock);
+
+ /*
+ * Remove @cgrp directory. The removal puts the base ref but we
+ * aren't quite done with @cgrp yet, so hold onto it.
+ */
+ dget(d);
+ cgroup_d_remove_dir(d);
+
+ /*
+ * Unregister events and notify userspace.
+ * Notify userspace about cgroup removing only after rmdir of cgroup
+ * directory to avoid race between userspace and kernelspace.
+ */
+ spin_lock(&cgrp->event_list_lock);
+ list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
+ list_del_init(&event->list);
+ schedule_work(&event->remove);
+ }
+ spin_unlock(&cgrp->event_list_lock);
+
/* tell subsystems to initate destruction */
for_each_subsys(cgrp->root, ss)
offline_css(ss, cgrp);
@@ -4409,34 +4437,15 @@
for_each_subsys(cgrp->root, ss)
css_put(cgrp->subsys[ss->subsys_id]);
- raw_spin_lock(&release_list_lock);
- if (!list_empty(&cgrp->release_list))
- list_del_init(&cgrp->release_list);
- raw_spin_unlock(&release_list_lock);
-
/* delete this cgroup from parent->children */
list_del_rcu(&cgrp->sibling);
list_del_init(&cgrp->allcg_node);
- dget(d);
- cgroup_d_remove_dir(d);
dput(d);
set_bit(CGRP_RELEASABLE, &parent->flags);
check_for_release(parent);
- /*
- * Unregister events and notify userspace.
- * Notify userspace about cgroup removing only after rmdir of cgroup
- * directory to avoid race between userspace and kernelspace.
- */
- spin_lock(&cgrp->event_list_lock);
- list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
- list_del_init(&event->list);
- schedule_work(&event->remove);
- }
- spin_unlock(&cgrp->event_list_lock);
-
return 0;
}
